Every once in a while, I read a paper that makes me scratch my head. Last week was just such a moment. The paper really needs no introduction. The title says it all: “Increasing volume of food by incorporating air reduces energy intake” [in dogs].
Let’s talk about obesity (again): If you read “Do you think I look fat in this collar?” you will remember that obesity is the most prevalent nutritional disorder in pet dogs today. Moreover, there is evidence that a substantial number of owners do not recognize overweight conditions in their dogs and even when they do, are unwilling or unable to comply with weight loss recommendations.
In their search to identify new approaches to weight control (preferably approaches that can be marketed into a new brand of dog food), some pet food companies have looked at the effects of diluting food calories. An example is increasing dietary fiber. This reduces the number of calories provided in a cup of food. Consuming foods that are high in non-fermentable fibers may also enhance feelings of satiety (fullness) in dogs, although the evidence for this effect is not conclusive. However, feeding high levels of dietary fiber causes increased defecation frequency and stool quantity, often producing voluminous poops that are loose and smelly, effects that most owners are not looking for in a dog food.
Recently, in their quest to find a canine version of the weight loss Holy Grail, researchers latched on to a nutrient that most of us would probably not even consider when thinking about keeping Muffin trim. (We would not consider it because it is actually not a nutrient).
The Study: A group of researchers at the Royal Canin Research Center, at the National College of Veterinary Medicine in France and at the University of Liverpool in the UK collaborated to study the effects of feeding a dry dog food formulated to contain more air (1). They wanted to determine if there was a satiety-producing effect of adding air to extruded kibbles, thereby increasing the volume that is fed whilst delivering the same number of calories. This is essentially a cheaper version of the “let’s add fiber to dog food to dilute its calories” approach.
To understand this concept, consider the density (weight/volume) of a cup of corn meal compared with the density of a cup of air-popped popcorn. Same food; more air in the latter than the former. As a result, the cup of popped corn will contain fewer calories and nutrients than the cup of ground corn meal. When we are talking about extruded dog food, this idea is quite easy to put into practice because varying extrusion conditions during processing can lead to different degrees of expansion in the end product. Highly expanded kibbles contain more air pockets, will feel lighter (because they are), and will provide fewer calories per cup than a food that has the same nutrient formulation but is less expanded. Compare the two examples below:
The food on the left is a very dense product and provides about 460 kcal/cup when fed to a dog. The food on the right is less dense (you can see the little air pockets in the kibbles), and provides about 320 kcal/cup when fed. (Note: Multiple factors, not only air, affect a food’s energy density. These include the food’s digestibility and fat content, among other attributes).
The Air-enhanced Food: The researchers created a test diet that was extruded to include a higher proportion of air than that which is typical. Simply expanding the kibbles to a greater degree and increasing its trapped air pockets resulted in a caloric density that was about half that of the control food. The control diet was a food that contained the same ingredients and nutrient profile, but less air. The researchers conducted three feeding trials:
- Experiment 1 measured the length of time that it took dogs to consume a meal that contained increasing proportions of the test diet while still providing the same number of calories. Therefore, because the test food contained less than half of the calories per cup than the control food, the amount of food that was fed more than doubled when the test diet was fed exclusively. Results: Not surprisingly, it took dogs longer to eat the larger meals of air-enhanced food than it took them to eat the smaller volume of food that they were given of the control diet. (In other words, it took the dogs longer to eat, um……more food). Although this sounds obvious, there is some evidence (in human subjects) that slowing down the rate of eating while consuming the same number of calories enhances satiety by increasing the release and effects of satiety-inducing and appetite-suppressing hormones.
- Experiment 2 fed the test food and the control food to a group of 10 adult Beagles and used a standard procedure used to measure satiety. This methodology involves offering dogs more food than they are expected to eat in sequential meals spaced one hour apart (kinda like “first breakfast and second breakfast” for Hobbit fans). Results: Adding air to food slightly enhanced feelings of satiety in dogs. This means that the dogs consumed a bit less food each day (and fewer calories) of the air-enhanced food when allowed to eat all that they desired than they did of the control food. This effect is similar to the expectation that consuming a high fiber food will lead to making one feel a bit more full and subsequently to consuming less food overall.
- Experiment 3 used the same protocol as Experiment 2 and compared the satiety-inducing effects of the test diet with a commercially available adult maintenance dog food. The commercial food provided more than 3 times the calories per cup as the test, air-enhanced food. Results: The results were similar to those of Experiment 2. Adding air (lots of it, by comparison) to a food moderately enhanced feelings of satiety in the dogs. I envision a group of over-stuffed Beagles, burping politely (and repeatedly….it is air after all), and saying “Really. No. I couldn’t eat another bite”.
The researchers concluded: “….results from the present study indicate that incorporating air into food provides a strategy to reduce energy [caloric] intake in dogs and, consequently could be a useful strategy for weight management in pets.” They also note that this study did not show whether or not dogs would reduce their intake of air-enhanced food to levels that would lead to weight loss nor did it measure effects for more than a few days. They assure us that such research is yet to come.
Draggin’ Out the Ol’ Box: Even if it can be shown that increasing the amount of air in a dog’s food enhances satiety, do we really need such a food? If one’s goals are to reduce a dog’s caloric intake and slow rate of eating, there are already effective approaches that owners can take. We can first select a high quality food (or home prepared diet) that is well-matched to our dog’s lifestyle and activity level. If a dog gains too much weight, we can reduce the amount that is fed or switch to a food that is still of high quality but is lower in fat (i.e. less energy dense without diluting calories). Increasing exercise through daily walks, engaging in a new dog training activity or sport, or teaching retrieve or “find it” games will all burn more calories and help increase a dog’s fitness level.
What about satiety? Is it true that feeding a larger volume of food or slowing the rate of eating will help our dogs to feel more satisfied? Perhaps. There is certainly some evidence to support this theory. However, while the hormonal changes associated with a slower rate of eating may enhance feelings of satiety, do we really need to inject air into our dog’s food to accomplish this? Many owners spread out their dog’s daily meal time by using a food delivery toy that their dog enjoys or feed using a “slow” bowl that is constructed to make the dog work a bit harder for his food. Feeding multiple small meals a day or floating dry food in warm water prior to feeding can be helpful to slow rate of eating as well.
Surely, we should not be expected to view injecting air into food as the new miracle weight loss approach for dogs. Are we really destined to see a new brand of dog food on the shelves selling under the marketing slogan of “Let Them Eat Air“?
Cited Study: Serisier S,Pizzagalli A, Leclerc L, Feugier A, Nguyen P, Biourge V, German AJ. Increasing volume of food by incorporating air reduces energy intake. Journal of Nutritional Science 2104; 3;e59:1-5.